Ozone layer is a thin blanket-like layer that spreads over the atmosphere of the earth.The ozone layer protects the surface of the earth and its phenomena from stray rays from the sun.It allows only the required doses of the Sun’s solar energy to reach the earth’s surface.Man has tried hard to deploy protective measures towards controlling the ozone layer from depletion,but this is so impossible to be achieved with the rapid growth of industries.Most factories release untreated effluents to the atmosphere which may be held in the atmosphere or react with other atoms to cause a great effect to the ozone layer with time.
Energy from the sun reaches the earth as infra-red,visible and ultra-violet(U.V) light.Among these forms of light from the sun,it is ultra-violet rays that are biologically proven as harmful beyond certain doses.This UV light can be classified in to three categories,namely:Ultra violet light type A(UV-A),ultra violet light type B(UV-B) and ultra violet light type C(UV-C).The wavelengh for UV-A ranges between 320 and 400 nanometers(nm).UV-B has the wavelength ranging from 290 and 320 nm.And finally,the wavelength of UV-C ranges between 190 and 290nm.Among these UV radiation categories,only UV-A and UV-B reaches the surface of the earth,where as UV-C is absorbed before it reaches the atmosphere,therefore it is the only harmless UV light rays to the earth and its occupants. Depletion of ozone layer has led to increased solar ultra violet(UV-B) radiation at earth’s surface.The ultra violet radiation is readily absorbed by living tissue,and since light at this wavelength has sufficient energy to break chemical bonds,it can be injurious to both plants,animals and human beings.
Effects of ozone layer depletion to human beings include:(i)Skin deterioration:This effect is not life-threatening since it only affects the outermost layer of the skin,hence affecting appearence.It is the most harmless effect of excess solar radiation as a result of ozone layer depletion.(ii)Skin cancer.There exist two main forms of skin cancer,namely: melanoma and non-melanoma.Melanoma is the most serious form of skin cancer.It’s often fatal.Non-melanoma is the most common form of skin cancer which damages the skin’s DNA. It has low fatality rate.(iii)Sun-evoked rash.(iv)Immune inhibition.(v)Cataracts.It accounts for the major causes of blindness in the world.Though surgery in developed countries has been success.
Effects of ozone layer depletion to plants include:Affects the physiological and developmental processes of plants such as yields,leaf size,photosynthesis rate,and resistance to diseases and insects.
Effects of ozone layer depletion to marine ecosystems:Planktons only respond to visible light energy but not ultra violet form of light.Planktons refer to the collection of micro-organisms that live in the water bodies including oceans,seas,lakes,ponds,among others.These are classfied into two types,namely Phytoplanktons and zooplanktons.Phytoplanktons are actually micro-organic plants,where as zooplanktons are micro-organic animals.Exposure of these planktons to excessive solar radiation,of course due to ozone layer depletion,their survival rates are drastically minimised.Early developmental phases of marine animals including fish becomes damaged.Larval development becomes impaired, and reproductive capacity becomes reduced.
Effects of ozone layer depletion to biogeochemical cycles:Excessive ultra violet rays reaching the earth’s surface alters the sources and sinks of greenhouses gases as well as chemically important trace gases such as carbondioxide,ozone and carbonmonoxide gases.
Effects of ozone layer depletion to other materials:Ultra violet rays especially type B(UV-B) affects synthetic polymers and some other materials.This limits the length of time for which they are useful outdoors.
The following are various causes of ozone layer depletion,an effect that has led to high rate of side effects to the earth’s surface as well as living things including human beings.(i)Chlorofluorocarbons(CFCs).Chlorofluorocarbons or CFCs are non-toxic and non-flammable. They contain fluorine atoms, carbon atoms and chlorine atoms. Man-made CFCs are the main cause of stratospheric ozone depletion. CFCs have a lifetime of about 50 years, and consequently one free chlorine atom from a CFC molecule can do a lot of damage, destroying ozone molecules for a long time. Although emissions of CFCs around the developed world have largely ceased due to international control agreements, the damage to the stratospheric ozone layer will continue for a number of years to come.The 5 main CFCs include trichlorofluoromethane ,dichloro-difluoromethane,trichloro-trifluoroethane ,dichloro-tetrfluoroethane and chloropentafluoroethane.
CFCs have been widely used as coolants in refrigeration and air conditioners, as solvents in cleaners, particularly for electronic circuit boards, as a blowing agents in the production of foam e.g. fire extinguishers and as propellants in aerosols. CFCs persists in the atmosphere long enough to diffuse upward into the stratosphere.Intense heat radiation from the sun breaks them up,releasing reactive chlorine atoms which destroy the ozone layer.These chlorine atoms are usually regenerated by various reactions in the atmosphere.For this reason,the atoms are capable of reacting with ozone layer over and over again.Whilst chlorine is a natural threat to ozone, CFCs which contain chlorine are a man-made problem. Although CFC molecules are several times heavier than air, winds mix the atmosphere to altitudes far above the top of the stratosphere much faster than molecules can settle according to their weight. CFCs are insoluble in water and relatively unreactive in the lower atmosphere but are quickly mixed and reach the stratosphere regardless of their weight. When UV radiation hits a CFC molecule it causes one chlorine atom to break away. The chlorine atom then hits an ozone molecule consisting of three oxygen atoms and takes one of the oxygen molecules, destroying the ozone molecule and turning it into oxygen. When an oxygen molecule hits the molecule of chlorine monoxide, the two oxygen atoms join and form an oxygen molecule. When this happens, the chlorine atom is free and can continue to destroy ozone.
(ii)Man-made halocarbon refregerators.Halocarbon is a generic term covering a number of human-produced gases all containing carbon and halogen.Examples of these halogen gases include:fluorine, chlorine or bromine atoms. Halocarbons include chlorofluocarbons (CFCs) and halons. The halocarnons were widely used for a variety of purposes such as propellants in aerosol cans. in the manufacture of soft and hard foams, in refrigeration and air conditioning, and as cleaning solvents. Consequently, they were increasing rapidly in the atmosphere.Halocarbons in the troposphere are inert, non-toxic. non-flammable,odourless and colourless. However, when they reach the stratosphere, particularly at and above the layer of maximum ozone, high-energy ultraviolet photons from the sun heats the halogenic carbons to free chlorine or bromine atoms. These atoms catalytically detach one oxygen atom from an ozone molecule, thus convert ozone to molecular oxygen,hence depleting the ozone layer.
(iii)Other ozone layer depleting substances include: Propellants and solvents;Ozone depleting chemicals such as carbon tetrachloride and trichloethane;Nitric oxide,chlorine radical and bromine radical.
Prevention of ozone layer depletion effects: Measures have been taken by various countries to phase down the use of CFCs, as well as other ozone depleting chemicals such as halons and other man-made halocarbons.Day-to-day activities that may help reduce the effects of excess solar radiation include:Seeking shade,wearing protective clothing,and sun glasses, using sunscreens: creams that repair uv-induced DNA damage,substances applied topically to the skin or eaten in the diet that protect against some of the detrimental effects of sun exposure.